Native Annual Plants Research Articles

First report of Puccinia recondita rust on native jewelweed (Impatiens capensis) in Pennsylvania.

Jewelweed (Impatiens spp., Balsaminaceae) is a common native annual plant within Pennsylvania wetland ecosystems, many of which are under threat from invasive non-native plants, and is an important wetland indicator plant (code FACW; facultative wetland). In May 2014, rust disease symptoms on native jewelweed (Impatiens capensis Meerb.) were observed within a small (0.1 ha) wet area in York County, southeastern Pennsylvania (39.9080648oN, -77.2472024oW). Rust symptoms were noted on most jewelweed plants within the wet area. Foliar symptoms included chlorosis and premature defoliation; infected stems were distorted. Infected leaves and stems contained orange, erumpent aecia with white fragmented peridia (Fig. 1). Symptomatic leaves and stem sections were collected from five infected plants within one small (5 X 5 m) plot in the center of the wet area and taken to the laboratory for microscopic observations and morphological measurements. Mean aecia diameter was 299.2 ± 55.0 µm (n = 60). Aeciospores were single-celled, orange, and generally globose (Fig. 2) with a mean diameter of 24.4 ± 1.4 µm, (n = 60). Disease symptomology and aecia morphology were consistent with Puccinia recondita Dietel & Holw. DNA extraction (from infected stem material), polymerase chain reactions, and DNA sequencing of the 28S region of the nuclear ribosomal DNA repeat was conducted following protocols in Aime (2006) and Aime et al. (2018). The sequence shares 99.34% identity (903 / 909 bp) with P. recondita (BPI 910319) collected in California (KY798399). A voucher specimen has been deposited in the Arthur Fungarium at Purdue University (PUR N24229) with corresponding 28S sequence (GenBank accession OR648406). P. recondita has been reported on native I. capensis in Indiana (Koslow and Clay 2010) and North Carolina (Grand 1985), but not in Pennsylvania to the best of our knowledge (Farr and Rossman 2022). If this rust disease becomes severe on native jewelweeds in Pennsylvania, it may adversely affect our ability to accurately classify native wetlands in the state. In addition, P. recondita is a heteroecious rust that is a major pathogen of grain crops of economic importance (i.e., wheat, barley, oats), which are grown in southeastern Pennsylvania near the infested area. Further research is warranted to understand if native, annual jewelweed can serve as a secondary or alternate host to cause rust disease in major cereal crops.

Consumer pressure and supplemental pollination mediate shrub facilitation of a native annual desert plant.

Shrubs are important factors in the assembly of desert plant and animal communities. By providing shelter and resources to other plants and animals, shrubs can change plant-animal interactions including those with consumers and pollinators. Here, we test the hypothesis that shrubs facilitate the reproduction of other desert plants by influencing pollination and compensation for consumer pressure. We used the known benefactor Larrea tridentata as our focal shrub species and the flowering annual Malacothrix glabrata as a potential protege in the Mojave Desert. We tested the effects of facilitation (shrub microsite), consumer pressure (both artificial folivory and florivory), and pollination (ambient or supplemented) on flower and seed production of the annual M. glabrata. We found that floral production and seed mass were similar between microsites but that pollen was limited under shrubs in the absence of any other manipulation. Plants under shrubs produced more flowers and seeds than in the open when folivory and florivory treatments were applied. Malacothrix glabrata experienced a cost to association with L. tridentata in terms of pollen limitation but plants were better able to compensate for consumer pressure under shrubs through increased flower and seed production when damaged. Therefore, association with shrubs involves a reproductive trade-off between costs to pollination and benefits to compensation for consumer pressure.

The spatial scale of adaptation in a native annual plant and its implications for responses to climate change.

Spatial patterns of adaptation provide important insights into agents of selection and expected responses of populations to climate change. Robust inference into the spatial scale of adaptation can be gained through reciprocal transplant experiments that combine multiple source populations and common gardens. Here, we examine the spatial scale of local adaptation of the North American annual plant common ragweed, Ambrosia artemisiifolia, using data from four common gardens with 22 source populations sampled from across a ∼1200km latitudinal gradient within the native range. We found evidence of local adaptation at the northernmost common garden, but maladaptation at the two southern gardens, where more southern source populations outperformed local populations. Overall, the spatial scale of adaptation was large-at the three gardens where distance between source populations and gardens explained variation in fitness, it took an average of 820km for fitness to decline to 50% of its predicted maximum. Taken together, these results suggest that climate change has already caused maladaptation, especially across the southern portion of the range, and may result in northward range contraction over time.

Climate warming threatens the persistence of a community of disturbance-adapted native annual plants.

With ongoing climate change, populations are expected to exhibit shifts in demographic performance that will alter where a species can persist. This presents unique challenges for managing plant populations and may require ongoing interventions, including insitu management or introduction into new locations. However, few studies have examined how climate change may affect plant demographic performance for a suite of species, or how effective management actions could be in mitigating climate change effects. Over the course of two experiments spanning 6 yr and four sites across a latitudinal gradient in the Pacific Northwest, United States, we manipulated temperature, precipitation, and disturbance intensity, and quantified effects on the demography of eight native annual prairie species. Each year we planted seeds and monitored germination, survival, and reproduction. We found that disturbance strongly influenced demographic performance and that seven of the eight species had increasingly poor performance with warmer conditions. Across species and sites, we observed 11% recruitment (the proportion of seeds planted that survived to reproduction) following high disturbance, but just 3.9% and 2.3% under intermediate and low disturbance, respectively. Moreover, mean seed production following high disturbance was often more than tenfold greater than under intermediate and low disturbance. Importantly, most species exhibited precipitous declines in their population growth rates (λ) under warmer-than-ambient experimental conditions and may require more frequent disturbance intervention to sustain populations. Aristida oligantha, a C4 grass, was the only species to have λ increase with warmer conditions. These results suggest that rising temperatures may cause many native annual plant species to decline, highlighting the urgency for adaptive management practices that facilitate their restoration or introduction to newly suitable locations. Frequent and intense disturbances are critical to reduce competitors and promote native annuals' persistence, but even such efforts may prove futile under future climate regimes.

Microhabitats associated with solar energy development alter demography of two desert annuals.

Political and economic initiatives intended to increase energy production while reducing carbon emissions are driving demand for solar energy. Consequently, desert regions are now targeted for development of large‐scale photovoltaic solar energy facilities. Where vegetation communities are left intact or restored within facilities, ground‐mounted infrastructure may have negative impacts on desert‐adapted plants because it creates novel rainfall runoff and shade conditions. We used experimental solar arrays in the Mojave Desert to test how these altered conditions affect population dynamics for a closely related pair of native annual plants: rare Eriophyllum mohavense and common E. wallacei. We estimated aboveground demographic rates (seedling emergence, survivorship, and fecundity) over 7 yr and used seed bank survival rates from a concurrent study to build matrix models of population growth in three experimental microhabitats. In drier years, shade tended to reduce survival of the common species, but increase survival of the rare species. In a wet year, runoff from panels tended to increase seed output for both species. Population growth projections from microhabitat‐specific matrix models showed stronger effects of microhabitat under wetter conditions, and relatively little effect under dry conditions (lack of rainfall was an overwhelming constraint). Performance patterns across microhabitats in the wettest year differed between rare and common species. Projected growth of E. mohavense was substantially reduced in shade, mediated by negative effects on aboveground demographic rates. Hence, the rare species were more susceptible to negative effects of panel infrastructure in wet years that are critical to seed bank replenishment. Our results suggest that altered shade and water runoff regimes associated with energy infrastructure will have differential effects on demographic transitions across annual species and drive population‐level processes that determine local abundance, resilience, and persistence.

Reciprocal facilitation between annual plants and burrowing crabs: Implications for the restoration of degraded saltmarshes

Abstract Increasing evidence shows that facilitative interactions between species play an essential role in coastal wetland ecosystems. However, there is a lack of understanding of how such interactions can be used for restoration purposes in saltmarsh ecosystems. We therefore studied the mechanisms of reciprocal facilitative interactions between native annual plants, Suaeda salsa, and burrowing crabs, Helice tientsinensis, in a middle‐elevation saltmarsh (with generally high plant density and moderate tides) in the Yellow River Delta of China. We investigated the relationship between the densities of the plants and crab burrows in different seasons. Then, we tested whether and how saltmarsh plants and crabs indeed facilitate each other in a series of field and laboratory experiments. Finally, we applied the results by creating a field‐scale artificial approach for microtopographic modification to restore a degraded saltmarsh. We found that the density of plant seedlings in spring was positively correlated with the density of crab burrows in the previous autumn; moreover, the density of crab burrows was correlated with the density of plants in summer. The concave–convex surface microtopography created by crabs promoted seed retention and seedling establishment of saltmarsh plants in winter and spring. These plants in turn facilitated crabs by inhibiting predators, providing food and reducing physical stresses for crabs in summer and autumn. The experimental removal of saltmarsh plants decreased crab burrow density, while both transplanting and simulating plants in bare patches promoted crabs. The microtopographic modification, inspired by our new understanding of the interactions between saltmarsh plants and crabs, showed that these degraded saltmarsh ecosystems can be restored by a single ploughing intervention. Synthesis. Our results suggest a reciprocal facilitation between annual plants and burrowing crabs in a middle‐elevation saltmarsh ecosystem. This knowledge yielded new restoration options for degraded coastal saltmarshes through the one‐time ploughing initiation of microtopographic variation, which could promote the re‐establishment of ecosystem engineers and lead to the efficient recovery of pioneer coastal vegetation and associated fauna.

Biogeomorphological processes and structures facilitate seedling establishment and distribution of annual plants: Implications for coastal restoration

Biogeomorphological processes and structures (BPS) can affect plant growth and community structure and promote landscape complexity in ecosystems. However, there is a lack of understanding of how BPS facilitates seedling establishment and distribution of annual plants and promotes the success of coastal restoration. We studied the relationships between seedling establishment of a native annual plant species (Suaeda salsa) and BPS resulting from crabs and plants in a middle elevation salt marsh with moderate tides (where inhabited generally high density of plants and crabs) in the Yellow River Delta of China. While there were many crabs but fewer plants in lower elevation areas with more frequent and stronger tides; and in higher elevation areas with weaker tides there were both fewer crabs and plants. Investigations and field manipulation experiments of microtopography, crabs and plants were conducted to determine if and how these BPS influenced seedling establishment and distribution under tidal influence in the middle elevation salt marshes. Results demonstrated that biogeomorphological structures, mainly concave hollows generated by crab burrowing and concave hollows around plant roots and stems under tidal influence, were associated with the trapping of seeds and influenced the establishment and distribution of seedlings. Additionally, upon senescence, maternal plants with unreleased seeds lodged on the ground and influenced seed retention and seedling establishment. The artificial concave hollows that were created experimentally also trapped many seeds and facilitated seedling establishment. Experimental plantings and creation of artificial hollow microtopography attracted crabs that created burrows, resulting in a positive feedback on seedling establishment. We used information obtained from the experimental component of the study to conduct a hollow microtopography manipulation to successfully restore degraded salt marshes. Understanding the associations between seedling establishment and biogeomorphological processes provides important insights for the utilization of natural or human ecosystem engineering to restore coastal vegetation ecosystems.

Plant-soil feedbacks under resource limitation may not contribute to the invasion by annual Asteraceae plants.

Changes in resource availability can alter plant growth, the influence of plants on soil characteristics, and, ultimately, plant-soil feedback (PSF). Previous studies often show that invasive plants can outperform native plants under high but not low resource conditions. However, it remains unclear whether under low resource conditions, invaders can outperform natives in the long term by generating more positive or less negative PSFs. Using three non-native invasive and three non-invasive native annual Asteraceae plants, we conducted a two-phase pot experiment, where in the first, conditioning generation plants were grown to induce changes in soil characteristics, and in the second, bioassay generation plants were regrown to evaluate how they respond to these soils. Half of the pots received a nutrient addition treatment in the conditioning generation. We found significant species-specific effects of conditioning on most of the soil characteristics, and some soil characteristics were significantly correlated with bioassay generation biomass of a subset of species, but neither species nor invasive or native status affected bioassay generation biomass. All invasive species generated neutral PSFs across soil nutrient conditions. The native Emilia sonchifolia tended to condition the soil that favored its own growth more than others, and under low nutrient conditions, the native Eclipta prostrata conditioned the soil that disfavored its own growth more than others. These results indicate that invaders may not outperform natives through PSFs under low resource conditions, and increasing resource availability may change the types of PSFs for some native but not invasive plants.

Effects of soil nutrients on reproductive traits of invasive and native annual Asteraceae plants

Effects of soil nutrients on reproductive traits of invasive and native annual Asteraceae plants

Evolutionary and plastic changes in a native annual plant after a historic drought.

Severe droughts are forecast to increase with global change. Approaches that enable the study of contemporary evolution, such as resurrection studies, are valuable for providing insights into the responses of populations to global change. In this study, we used a resurrection approach to study the evolution of the California native Leptosiphon bicolor (true babystars, Polemoniaceae) across populations differing in precipitation in response to the state's recent prolonged drought (2011–2017). In the Mediterranean climate region in which L. bicolor grows, this historic drought effectively shortened its growing season. We used seeds collected both before and after this drought from three populations found along a moisture availability gradient to assess contemporary evolution in a common garden greenhouse study. We coupled this with a drought experiment to examine plasticity. We found evolution toward earlier flowering after the historic drought in the wettest of the three populations, while plasticity to experimental drought was observed across all three. We also observed trade‐offs associated with earlier flowering. In the driest population, plants that flowered earlier had lower intrinsic water‐use efficiency than those flowering later, which was an expected pattern. Unexpectedly, earlier flowering plants had larger flowers. Two populations exhibited evolution and plasticity toward smaller flowers with drought. The third exhibited evolution toward larger flowers, but displayed no plasticity. Our results provide valuable insights into differences among native plant populations in response to drought.

Influence of Groundcover Vegetation, Soil Physicochemical Properties, and Irrigation Practices on Soil Fungi in Semi-arid Vineyards

Although plants are known to have a strong influence on soil biota, the effect of groundcover vegetation in perennial cropping systems on soil fungi has been little explored. We surveyed extensively managed vineyards to determine how plant community functional characteristics, soil factors, and irrigation management related to the abundance of two guilds of soil fungi that may play a role in plant-soil feedback (entomopathogenic fungi represented by Beauveria bassiana, and the pathogenic species complex, Ilyonectria spp.). We found that plant community characteristics were related to fungal abundance for both fungi assayed. Beauveria bassiana increased with native species, annual plants, and legumes consistently across sampling periods. Ilyonectria spp. increased with the abundance of forbs and exotic species, though only the relationship with forbs was consistent across sampling periods. Both fungal guilds increased with increasing soil organic matter. The use of dual or sprinkler irrigation systems also increased Beauveria bassiana and Ilyonectria spp. in vineyard soils. Overall, groundcover vegetation played a significant role in driving abundance of these important groups of soil fungi. Groundcover management may therefore be a viable tool to manipulate soil fungi with the potential for improving ecosystem services such as conservation biological control of soil dwelling insect pests and deterring pathogens in perennial cropping systems.

Effects of nutrient addition and clipping on biomass production of invasive and native annual Asteraceae plants

SummaryInvasive plants dominate many habitats and cause significant harm to native plants, agriculture and the wider environment. Clipping by mowing machines has been a common method to control invasive plants, but whether it can reduce the performance of invaders and increase the performance of co‐occurring natives is not known. This study examined the effects of soil nutrient conditions and clipping on the performance of three invasive and three co‐occurring native annual Asteraceae plants under either isolated or competitive conditions. Clipping tended to reduce the aboveground biomass of the invasive plants more than that of the native plants under low, but not under high nutrient conditions. However, invasive plants still produced an aboveground biomass equal to, or larger than, that of native plants under the low nutrient and clipping treatment combination. Nutrient addition increased the aboveground biomass of the invasive plants more than that of the native plants, although this was only marginally significant under competitive conditions. Clipping did not reduce the performance advantage of invaders over natives under high soil nutrient conditions. The ability of invaders to benefit more from nutrient addition, along with its ability to perform equally well, or better than, the native plants after human mechanical control (i.e. clipping), may explain their high abundance and dominance in many habitats.

Living in the city: urban environments shape the evolution of a native annual plant.

Urban environments are warmer, have higher levels of atmospheric CO2 and have altered patterns of disturbance and precipitation than nearby rural areas. These differences can be important for plant growth and are likely to create distinct selective environments. We planted a common garden experiment with seeds collected from natural populations of the native annual plant Lepidium virginicum, growing in five urban and nearby rural areas in the northern United States to determine whether and how urban populations differ from those from surrounding rural areas. When grown in a common environment, plants grown from seeds collected from urban areas bolted sooner, grew larger, had fewer leaves, had an extended time between bolting and flowering, and produced more seeds than plants grown from seeds collected from rural areas. Interestingly, the rural populations exhibited larger phenotypic differences from one another than urban populations. Surprisingly, genomic data revealed that the majority of individuals in each of the urban populations were more closely related to individuals from other urban populations than they were to geographically proximate rural areas - the one exception being urban and rural populations from New York which were nearly identical. Taken together, our results suggest that selection in urban environments favors different traits than selection in rural environments and that these differences can drive adaptation and shape population structure.

Why are native annual abundances low in invaded grasslands? Testing the effects of competition and seed limitation

Competitive suppression of native species has long been considered among the most important mechanisms allowing exotic plants to dominate some communities, but recent work has focused attention on the potential role of native seed limitation. We tested effects of competition from exotic annual grasses and seed limitation on the abundances of four native annual plants in invaded southern California grassland for two different years. Both initial responses and effects still present 1–3 years later were measured. In the wetter year of 2006, all four native species (Amsinckia menziesii var. intermedia, Phacelia distans, Camissonia bistorta and Clarkia purpurea ssp. quadrivulnera) increased in abundance with exotic grass removal, and two (Clarkia and Camissonia) responded significantly to seed addition. We observed limited treatment effects during the much drier growing season of 2007. By 2008–2009, any initial effects of exotic grass removal had disappeared. However, for both the 2006 and 2007 experiments seeding significantly increased native cover in 2009, independent of initial grass removal. Abundances of both Amsinckia and Phacelia, but not Camissonia or Clarkia, were significantly higher in seeded plots during 2008–2009. These delayed responses may have resulted from seed dormancy. Our results support the importance of both competition with exotics and seed limitation in determining native annual community composition of California grasslands. An interesting future question is whether traits related to resource use or germination phenology may predict differences in native species interactions with exotic grasses.

Bidirectional recovery patterns of Mojave Desert vegetation in an aqueduct pipeline corridor after 36 years: II. Annual plants

We studied recovery of winter annual plants in a 97-m wide disturbed aqueduct corridor in the Mojave Desert 36 years after construction. We established plots at 0, 20, and 40 m from the road verge at the corridor center and at 100 m in undisturbed vegetation. We recorded 47 annual species, of which 41 were native and six were exotic. Exotic species composed from 64 to 91% of total biomass. We describe a bilateral process of recovery: from the road verge to the outward edge of the corridor and from undisturbed habitat into the corridor. Native annual plants significantly increased in richness from road verge to undisturbed vegetation, but not in density, biomass, or cover. In contrast, exotic annual plants increased in density, biomass, cover and richness with increasing distance from the road verge. The species of colonizing shrubs and type of canopy cover affected density, biomass, and richness of annuals. Species composition of native annuals differed significantly by distance, suggesting secondary succession. In general, native annuals were closer to achieving recovery on the 40-m plots than at the road verge. Recovery estimates were in centuries and dependent on location, canopy type, and whether considering all annuals or natives only.

Enhancing Quality of Desert Tortoise Habitat: Augmenting Native Forage and Cover Plants

Abstract Vegetation in habitat of the federally listed desert tortoise Gopherus agassizii in the Mojave and western Sonoran Desert is now partly or mostly dominated by nonnative annual plants. To improve forage quality and augment availability of perennial cover plants, we tested seeding (pelletized or bare seeding), watering, and fencing for increasing a native annual forage species (desert plantain Plantago ovata), a perennial forage species (desert globemallow Sphaeralcea ambigua), and two shrub species (cheesebush Hymenoclea salsola and winterfat Krascheninnikovia lanata) that provide cover in desert tortoise habitat of southern Nevada. Treatments were ineffective at establishing the perennial species, even though greenhouse assays confirmed that some bare and pelletized seeds were germinable. In contrast, pelletized seeding quadrupled the density of desert plantain compared with not seeding or seeding untreated seed by the end of the first year (autumn 2013). Fencing tripled density of desert plantain to 17 plants/m2. Pelletized seeding plus fencing produced a desert plantain density of 39 plants/m2, the highest average density among all treatment combinations. The positive effect of fencing persisted until at least the second year after treatment (autumn 2014). Augmenting native annual forage plants favored by desert tortoises is feasible.

A mechanistic study of plant and microbial controls over R* for nitrogen in an annual grassland.

Differences in species' abilities to capture resources can drive competitive hierarchies, successional dynamics, community diversity, and invasions. To investigate mechanisms of resource competition within a nitrogen (N) limited California grassland community, we established a manipulative experiment using an R* framework. R* theory holds that better competitors within a N limited community should better depress available N in monoculture plots and obtain higher abundance in mixture plots. We asked whether (1) plant uptake or (2) plant species influences on microbial dynamics were the primary drivers of available soil N levels in this system where N structures plant communities. To disentangle the relative roles of plant uptake and microbially-mediated processes in resource competition, we quantified soil N dynamics as well as N pools in plant and microbial biomass in monoculture plots of 11 native or exotic annual grassland plants over one growing season. We found a negative correlation between plant N content and soil dissolved inorganic nitrogen (DIN, our measure of R*), suggesting that plant uptake drives R*. In contrast, we found no relationship between microbial biomass N or potential net N mineralization and DIN. We conclude that while plant-microbial interactions may have altered the overall quantity of N that plants take up, the relationship between species' abundance and available N in monoculture was largely driven by plant N uptake in this first year of growth.

The germination strategies of widespread annual plants are unrelated to regional climate

AbstractAimEnvironmentally cued germination and seed banking are strategies employed by annual plants to persist in unpredictable climates. Moreover, such strategies may be key to persistence under more extreme and variable future climates. In regions with a mediterranean climate, cold‐cued germination can allow populations to avoid germinating under unfavourable conditions and seed banks can buffer population growth in the face of inter‐annual climate variability. Using widespread native annual plant species in the California Floristic Province (CFP), we ask: (1) How common are cold‐cued germination and persistent seed banks? (2) Does the prevalence of cold‐cued germination and seed bank maintenance shift predictably with climate? (3) Are germination strategies taxonomically linked?LocationCalifornia, USA.MethodsWe assessed seed bank persistence and temperature‐cued germination in c. 175 populations of 42 species (eight families) from across California in the 2006 growing season. We then tested for evidence that the prevalence of these adaptations correlated with latitude, increasing climate variability and taxonomy.ResultsOnly 19% of populations had significantly cold‐cued seed germination and only 52% of populations had detectable seed banks. There were no significant relationships between the prevalence of cold‐cued germination and any climate factor. Seed banking was significantly more common in regions with warm, dry conditions in the preceding year, but was not related to long‐term climate averages. Variance in temperature‐cued germination was best explained at the species level, with no variance explained by family.Main conclusionsOur results suggest that germination of annual plants in the CFP is dominated by general risk aversion strategies rather than locally adaptive strategies linked to long‐term climate factors. High germination variability within and among populations, coupled with increased seed banking under less favourable conditions, suggests that germination strategies are unlikely to limit this flora's persistence under an increasingly harsh and unpredictable climate.

Using native annual plants to restore post-fire habitats in western North America

Increasing fire frequencies and uncharacteristic severe fires have created a need for improved restoration methods across rangelands in western North America. Traditional restoration seed mixtures of native perennial mid- to late-seral plant species may not be suitable for intensely burned sites that have been returned to an early-seral condition. Under such conditions, native annual plant species are likely to be more successful at becoming established and competing with exotic annual plant species, such as Bromus tectorum L., for resources. We used a field study in Colorado and Idaho, USA, to test the hypothesis that native annual plant species are better suited to post-fire restoration efforts compared with perennial plant species that are commonly used in traditional seed mixtures. Replicated test plots at three post-fire sites were assigned one of four treatments: (1) native annual seed mixture, (2) standard perennial seed mixture, (3) combination of annual and perennial and (4) an unseeded control. Seeding native annuals with perennials resulted in a slight reduction in exotic plant cover, suggesting that it is potentially beneficial to include native annual plant species in restoration seed mixtures.

The impact of habitat fragmentation on fitness-related traits in a native prairie plant,Chamaecrista fasciculata(Fabaceae)

Loss and fragmentation of the native prairies in the Midwestern United States have resulted in isolated and smaller habitats and populations. The populations remaining in these prairies are expected to show a decline in the extent of genetic variation and an increase in genetic drift load (accumulation of deleterious recessive alleles due to genetic drift) in fitness-related traits. Using complementary greenhouse experiments, we tested whether these expected changes have occurred in the native annual prairie plant Chamaecrista fasciculata. In the first experiment, open pollinated C. fasciculata seeds from 12 prairie fragments representing a range in area of habitat were grown in competition with Schizachyrium scoparium to determine if there are changes in plant vigour with changes in fragment size and corresponding changes in population size. Plants from smaller prairie fragments exhibited a slight but significant decline in biomass, suggesting an increase in genetic drift load. In the second experiment, a formal genetic crossing design of four prairie fragment populations was used to estimate quantitative genetic diversity and genetic drift load. We did not find extensive quantitative genetic variation, but we did find a strong effect of genetic drift load on five traits in this experiment. Our overall conclusion is that a decline in relative-fitness traits in smaller prairie fragments is probably associated with fixation of deleterious alleles due to more isolated and smaller populations, i.e. genetic drift load.